Folia biologica et geologica

Growing stock of tree and shrub species across elevation zones in Slovenia: comparative analysis and developmental characteristics

Anže Martin Pintar, Andreja Ferreira, Gal Kušar, Mitja Skudnik, Luka Krajnc — Tue, 19 May 2026 00:00:00 +0200

Slovenian forests are among the most species-rich in Europe, with 71 native tree species recorded. Despite this high diversity, two species—European beech (Fagus sylvatica) and Norway spruce (Picea abies)—dominate the growing stock, together accounting for 60% of the total volume. The growing stock of trees and shrubs above the 10 cm DBH (diameter at breast height) threshold increases with elevation, with the highest elevation zone reaching 398 m³/ha. In contrast, the Shannon–Wiener diversity index for trees and shrubs above 10 cm DBH decreases as elevation increases. A similar pattern is observed for the Shannon–Wiener index of small trees and shrubs (below the 10 cm DBH threshold), although values in the lowest elevation zone are slightly lower. The proportion of Norway spruce in the growing stock of trees above 10 cm DBH increases markedly with elevation, rising from 10.2% in the lowest elevation zone (<300 m) to 49.4% in the highest zone. In recent years, European beech has become the dominant species in the growing stock of both trees and shrubs above 10 cm DBH, as well as small trees and shrubs below 10 cm DBH, indicating a likely further increase in the proportion of beech in future growing stock development. In elevation zones below 700 m, the growing stock of small trees and shrubs contains a substantially higher proportion of thermophilous broadleaved species—particularly manna ash (Fraxinus ornus), hop hornbeam (Ostrya carpinifolia), the non-native black locust (Robinia pseudoacacia), and shade-tolerant hornbeam (Carpinus betulus)—compared to their proportion in the growing stock of trees and shrubs above 10 cm DBH. In the growing stock of small shrubs across Slovenia and within all elevation zones, common hazel (Corylus avellana) predominates. Its growing stock proportion is highest in the 700–1000 m elevation zone (91.3%) and lowest in the lowest elevation zone (61.9%).

Comparison of two methods for measurment of stomata in pedunculate and sessile oak

Tanja Mrak, Jožica Gričar — Mon, 06 Jul 2026 00:00:00 +0200

Stomatal traits, such as density and size, significantly influence gas exchange; therefore, their analysis is essential for understanding plant physiology, their adaptation to environmental conditions, and their responses to climate change. The aim of this study was to determine whether manual measurements of stomata in tree seedlings could be replaced by automated measurements, which would substantially increase the number of samples that can be analysed due to time savings. Epidermal imprints of stomata were prepared from seedlings of pedunculate oak and sessile oak growing at the same site. Ten randomly selected micrographs of the preparations at 200 × and 400 × magnification per species were used to analyse the number of stomata as well as the length and width of guard cells and stomatal pore, using both manual measurements in ImageJ and automated measurements in StoManager1. The results were statistically evaluated. No statistically significant differences between the two methods were found for measurements of stomatal number. Bland–Altman analysis showed good agreement between manual and automated measurements. Although the automated method slightly overestimated the number of stomata, the error was small. For size measurements, statistically significant differences between the two methods were observed, and Bland–Altman analysis revealed deviations between the methods at larger size ranges of the measured structures. Regression analysis indicated that agreement between manual and automated measurements was reasonably reliable within the size range of 20–25 µm (larger structures were not measured), but decreased with decreasing structure size, most likely due to image segmentation in the automated method and the associated less precise edge detection. In small structures, even minor segmentation differences can lead to larger errors. On the other hand, manual measurements in microscopy images can also become increasingly subjective as the size of structures decreases. Our results suggest that automated measurements using StoManager1 represent a suitable alternative to manual measurements of stomatal number/ density and dimensions of larger structures within the stomatal complex for the selected tree species.

Morphological variation of Betula pendula and betula pubescens leaves in south-eastern Europe

Mon, 06 Jul 2026 00:00:00 +0200

Birch species (Betula pendula Roth and Betula pubescens Ehrh.) are ecologically important components of temperate and boreal forests, exhibiting considerable morphological variability across their distribution ranges. This study aimed to assess leaf morphological variation among natural Betula populations in Bosnia and Herzegovina and Slovenia and to examine its relationship with environmental and climatic factors.

Leaves were collected from 39 populations (31 in Bosnia and Herzegovina and eight in Slovenia) during 2020–2022. Ten trees per population were sampled, with 30 leaves collected from each tree. In total, 11,700 leaves were analyzed. Morphometric analyses included measured, assessed, counted, and derived leaf traits. Descriptive statistics, nested analysis of variance, population differentiation coefficients, Pearson correlations, principal component analysis (PCA), and cluster analysis (UPGMA) were applied. Relationships between morphological traits and climatic variables were evaluated using bioclimatic data from the WorldClim database.

The results revealed substantial phenotypic variability in leaf morphology among the studied populations. The first two principal components explained 73.2% of the total variation, with leaf size parameters representing the dominant axis of differentiation. Cluster and PCA analyses indicated clear regional structuring, with Slovenian populations forming a distinct group from most populations in Bosnia and Herzegovina. Qualitative traits such as leaf shape, margin, pubescence, and texture showed significant heterogeneity among populations. Leaf pubescence was confirmed in two populations previously identified as B. pubescens (Han Kram and Mokro 2). Strong correlations were observed between leaf morphological traits and climatic variables, particularly mean annual temperature, which showed a strong influence on leaf dimensions.

Overall, the findings highlight pronounced morphological diversity in Betula populations and suggest that environmental gradients, particularly temperature, play a key role in shaping leaf morphological variation in south-eastern Europe.